A major advantage of a digital system is that a discreet command issued to a digital reacting device results in a single discreet motion without the use of secondary measurements and feedback loops. A number of rotational action devices are in current use. They include low torque electrical motors, medium torque device such as geared electrical motors, high torque pneumatic motors and very high torque hydraulic devices. With the exception of electrical stepping motors, all of these action devices require feedback systems to determine the motor shaft position, compare the actual position to the required position and through a feedback loop generate new commands to change the motor shaft position until the desired position is reached. When high torques are required, there is currently no satisfactory alternative to the use of analog devices. The torque of an electrical stepping motor torque can be increased by the use of various gear drivers. However, this approach is not suitable for usages in which a torque of several hundred inch pounds are required, or wherein rapid response at a high torque is required.
Various known or proposed drive systems present in the patent literature, which should be considered for the purpose of putting the present invention into proper perspective relative to the prior art, are shown by the following U.S. Pat. Nos.: No. 676,305, granted June 11, 1901 to Albert G. Davis; No. 1,436,245, granted Nov. 21, 1922 to Kurt M. Geisler; No. 1,886,040, granted Nov. 1, 1932, to Edwin F. Moodyman; No. 2,056,719, granted Oct. 6, 1936, to John F. Gelnaw; No. 2,617,949, granted Nov. 11, 1952, to George H. Leland; No. 2,706,259, granted Apr. 12, 1955, to Walter H. Wight; No. 2,851,619, granted Sept. 9, 1958, to Walter A. Jones; No. 2,900,961, granted Aug. 25, 1959, to Chien-Bor Sung; No. 3,075,504, granted Jan. 29, 1963, to Richard Vogel; No. 3,328,656, granted June 27, 1967 to Gene M. Dotson; No. 3,424,059, granted Jan. 28, 1969, to Ci Conner et al; No. 3,473,440, granted Oct. 21, 1969, to Donald Firth et al; No. 3,599,536, granted Aug. 17, 1971, to Lester L. Meyers; No. 3,661,059, granted May 9, 1972, to John M. Hunter et al; No. 3,676,719, granted July 11, 1972, to Angelo A. Pecci; No. 3,796,525, granted Mar. 12, 1974, to John B. Kilmer; No. 3,848,515, granted Nov. 19, 1974, to Bayard G. Gardineer et al; No. 4,012,675, granted Mar. 15, 1977, to Everett E. Schulze, Jr.; No. 4,066,002, granted Jan. 3, 1978, to James M. Eastland; and No. 4,068,560, granted Jan. 17, 1978, to George Orloff et al. Also to be considered, is British No. 961,339, granted June 17, 1964, to Donald Firth et al.